Thousands of women with breast cancer could avoid the debilitating effects of chemotherapy thanks to breakthrough genetic testing that can predict relapse risk within just two weeks of starting treatment. Two major research developments are transforming how clinicians approach breast cancer care, offering more personalized treatment strategies that could spare patients from unnecessary side effects while ensuring those at highest risk receive appropriate intensive therapy.
Revolutionary Two-Week Prediction Test
Scientists from The Institute of Cancer Research, London, have identified a method to predict breast cancer relapse risk using just two weeks of hormone therapy before surgery. The approach focuses on oestrogen receptor positive, human epidermal growth factor receptor 2 positive (ER+/HER2+) breast cancer, which accounts for 200,000 cases per year worldwide and represents one in 10 cases of breast cancer.
The research team analyzed tumor samples from 213 patients participating in the phase III POETIC trial, examining how tumors respond to short-term hormone therapy. Their findings, published in eBioMedicine, revealed that hormone therapy can alter tumor subtypes within just two weeks, providing crucial information for treatment decisions.
"To deliver truly personalized care, we need to refine how we classify breast cancer, so that each patient receives the treatment most likely to benefit them," said Dr. Maggie Cheang, leader of the ICR-CTSU Integrative Genomic Analysis in Clinical Trials Team. "This insight helps us identify which patients are likely to respond well and which may show early signs of treatment resistance, offering the opportunity to tailor treatment strategies sooner."
Tumor Subtype Shifts Guide Treatment Decisions
The research focused on two breast cancer subtypes: Luminal A and Luminal B. After two weeks of hormone therapy, 28% of tumors shifted from the more aggressive Luminal B subtype to the less aggressive Luminal A subtype, suggesting the treatment was working effectively.
Tumors that remained Luminal A after treatment—representing 19% of analyzed cases—were associated with the lowest risk of relapse. These patients, along with those whose tumors shifted to Luminal A, can continue with standard five-year hormone therapy.
However, patients with Luminal B tumors that did not change after short-term hormone therapy faced the highest relapse risk. These patients, accounting for 6% of the study population, were at least 1.5 times more likely to experience cancer recurrence and require more intensive treatments such as CDK4/6 inhibitors.
MammaPrint Test Transforms Treatment Landscape
Complementing this research, the MammaPrint genetic test has demonstrated remarkable success in identifying patients who can safely avoid chemotherapy. This sophisticated test analyzes the activity of 70 genes within breast cancer tissue and has been validated through a milestone study of 6,700 women.
The test revealed that almost half of women with early-stage breast cancer possess a low genetic risk of recurrence. Most significantly, 20% of patients previously classified as "high risk" using standard measures were reclassified as "low risk" by the genetic test, allowing them to avoid chemotherapy and its severe side effects.
"Understanding the genetics of a given cancer means that your physician has a better sense of what is going on in your unique case," explained Dr. Laura Esserman, a leading breast cancer specialist. "We can now comfortably say to many women that surgery and radiation, and then hormone therapy, will be sufficient."
Personalized Treatment Approach
The MammaPrint test is available for women with stage I or II breast cancer, including those with invasive tumors less than 5 centimeters in size, regardless of estrogen-receptor status. Instead of chemotherapy, low-risk patients can be treated with hormone therapy using medications like tamoxifen or anastrozole—daily pills taken for several years that, while not without side effects, are significantly less debilitating than chemotherapy.
This represents a fundamental shift from traditional treatment decisions based solely on tumor size, hormone receptor status, and lymph node involvement. Genetic risk scores are revolutionizing the treatment model by providing more precise risk assessment.
Clinical Impact and Future Implications
Professor Kristian Helin, Chief Executive of The Institute of Cancer Research, emphasized the broader significance of this molecular approach: "We have long moved past defining cancer solely by where it starts in the body—we now know that its complex molecular characteristics will drive its behavior. By decoding the underlying biology of tumors, we can tailor treatments to individual patients."
The research was funded by multiple organizations including The Institute of Cancer Research, Breast Cancer Now, NanoString, and the National Institute for Health and Care Research (NIHR) Biomedical Research Centre. The POETIC trial was co-sponsored by the ICR and The Royal Marsden NHS Foundation Trust.
Professor Marian Knight, Scientific Director for NIHR Infrastructure, noted the broader healthcare implications: "The insights that the researchers at The Institute of Cancer Research have uncovered in this study will help clinicians deliver more personalized breast cancer care that will be transformative for some patients, saving them from unnecessary treatments and their side effects."
As genetic testing continues to advance, these developments mark a significant step toward truly personalized cancer care, offering hope for thousands of women facing breast cancer diagnosis while ensuring that treatment intensity matches individual risk profiles.
